Compilare: main.cpp: In function 'int main()': main.cpp:13:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.length();i++){ ~^~~~~~~~~~~ main.cpp:14:11: warning: array subscript has type 'char' [-Wchar-subscripts] c[s[i]]++; ^ main.cpp:16:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.length();i++){ ~^~~~~~~~~~~ main.cpp:17:14: warning: array subscript has type 'char' [-Wchar-subscripts] if(c[s[i]]>=2){ ^